1. Field of the Invention
The present invention relates to a code reading method and device for a recording material roll. More particularly, the present invention relates to a code reading method and device for a recording material roll according to which an information code can be read with high precision.
2. Description Related to the Prior Art
Printers known in the art includes a photographic printer, thermal printer and the like. A recording sheet roll is used, and consists of a roll of continuous recording sheet such as photographic paper or thermosensitive recording sheet. After the printing, the continuous recording sheet is cut into each sheet by one image frame. The continuous recording sheet has photo sensitivity, optical fixability or the like. The recording sheet roll is set in a printer in a state contained in a supply magazine which is moisture-proof and shields ambient light.
Any type of thermosensitive recording sheet is changeable in density according to heat sensitivity. Also, there is a sticker type recording sheet well-known in the art. In general, the sticker type is used specially for printing thumbnail images arranged in a matrix form. Therefore, the recording sheet roll has an information code. In the recording sheet roll, a winding core is used and adapted to wind the recording sheet in a roll form. The information code is formed on an end surface of the winding core, and represents information such as a type, heat sensitivity, name of the manufacturer or the like of the recording sheet. The printer includes a code reading device for reading the information code, and determines printing conditions according to the information.
The information code is constituted by one start indicia and a plurality of data indicia. The start indicia has a size different from, or greater than, each of the data indicia, and is adapted to designate a position of starting reading of the data indicia. The data indicia are binary signs arranged at a predetermined pitch in a ring shape. Any of the start indicia and the data indicia are printed black in contrast with a white color of the end surface of the winding core.
To read the information code, a reading photo sensor is used and scans plural indicia in their arranging direction in rotation of the winding core and advancing the recording sheet. At first, the start indicia is designated, and then positions of the data indicia by referring to the start indicia. If one data indicia exists in each of the positions, then value of one (1) is retrieved. If no data indicia exists in one of the positions, then value of zero (0) is retrieved.
In a line printing type of printer, the recording sheet must be advanced at a constant speed irrespective of the amount of the remainder of the recording sheet. A supply roller is caused to contact the peripheral surface of the recording sheet roll about the winding core without directly controlling the winding core. The supply roller is driven at a constant speed to rotate the recording sheet roll. Thus, a roll diameter of the recording sheet roll changes with changes in the remaining amount of the recording sheet. An amount of advancing the recording sheet per one rotation of the winding core decreases in the course of a decrease in the roll diameter of the recording sheet roll. It is necessary to predetermine a rotating amount of the winding core for reading the information code in consideration of the maximum diameter of the recording sheet roll. When the recording sheet roll comes to have a very small diameter with a decrease in the recording sheet, a considerably high number of rotations must be made. Also, a process of detecting the start indicia is very complicated.
In a prior technique, a maximum detected size of the indicia is extracted from plural detection signals from the reading sensor. An indicia associated with the maximum detected size is determined as the start indicia. The roll diameter of the recording sheet is obtained according to the size of the start indicia, to designate a position of each of the data indicia. However, this technique requires high precision of detecting the size of the start indicia and the indicia positions. There is a serious problem in occurrence of jitter or fluctuation in circuits in a manner inconsistent to keeping precision in designating the start indicia. Errors in positions to read data are likely to occur, to lower precision in the detecting the information code.
In view of the foregoing problems, an object of the present invention is to provide a code reading method and device for a recording material roll according to which precision in reading an information code can be kept high.
In order to achieve the above and other objects and advantages of this invention, a code reading device for a recording material roll is provided, the recording material roll including a winding core, a recording material wound about the winding core, and an information code disposed on a surface of the winding core in an arc shape, the information code including plural data indicia arranged serially, and a start indicia disposed between beginning and ending ones of the plural data indicia, and having a size greater than each of the data indicia in an arranging direction thereof. The code reading device includes a rotating mechanism for rotating the recording material roll at a constant peripheral speed in a winding direction of the recording material. A reading sensor reads the plural data indicia and the start indicia. A timer measures passage time during which plural indicia in the information code pass the reading sensor while the recording material roll makes one rotation and thereafter rotates for a predetermined time. A controller checks the passage time of each of the plural indicia to determine one of the plural indicia as the start indicia, so as to determine remaining ones of the plural indicia as the data indicia to read the information code.
The plural data indicia have respectively a dot shape or bar shape, are arranged in a predetermined number of digits, have either high density or low density, and represent binary data.
The timer measures first elapsed time elapsed while the recording material roll makes one rotation. The controller obtains expected elapsed time related to passage of the start indicia according to a size of the start indicia and the first elapsed time, and checks whether the passage time of each of the plural indicia comes up to the expected elapsed time, wherein one of the plural indicia is determined as the start indicia when the passage time of the one indicia comes up to the expected elapsed time.
Furthermore, a front edge sensor detects a front edge of the recording material for at least two times while the recording material roll rotates. The timer measures the first elapsed time by measuring time between two successive output signals from the front edge sensor.
The controller extracts a longest passage time among plural values of the passage time measured from respectively the plural indicia in the information code, to compare the longest passage time with the expected elapsed time.
Start indicia passage time elapses while the start indicia passes the reading sensor, the start indicia passage time is changeable with a diameter of the recording material roll, and the predetermined time is a maximum value of the start indicia passage time.
The controller determines the one indicia in the plural indicia as the start indicia if a condition
(1xe2x88x92xcex2)xc2x7SMT1xe2x89xa6Tmaxxe2x89xa6(1+xcex2)xc2x7SMT1
is satisfied, wherein SMT1 is the expected elapsed time, Tmax is the longest passage time, and xcex2 is a small tolerable error.
The information code is formed on an end surface of the winding core.
In a preferred embodiment, the information code is formed on an inner surface of the winding core. Furthermore, first and second holder bodies are secured to respectively first and second ends of the winding core. First and second support shafts are disposed stationarily, for supporting respectively the first and second holder bodies in a rotatable manner. The reading sensor is secured to the first support shaft.
In another preferred embodiment, the information code is preprinted on the surface of the winding core.
In a further preferred embodiment, the recording material roll further comprises a code sticker previously provided with the information code, and secured to the surface of the winding core.
In still another preferred embodiment, a diameter of the recording material roll is changeable from a maximum diameter Dmax to a minimum diameter Dmin. The data indicia has a size LDM, the start indicia has a size LSM, and satisfies a condition of:
LSMxc2x7(Dmin/Dmax) greater than LDM. 
Start indicia passage time elapses while the start indicia passes the reading sensor, data indicia passage time elapses while each of the data indicia passes the reading sensor. The start indicia passage time and the data indicia passage time are changeable with a diameter of the recording material roll, and a minimum value of the start indicia passage time is longer than a maximum value of the data indicia passage time. The checking step includes comparing the passage time of each of the plural indicia with reference time, the reference time being predetermined between the minimum value of the start indicia passage time and the maximum value of the data indicia passage time, the one indicia being determined as the start indicia if the passage time of the one indicia is equal to or more than the reference time.